Piezoelectric ignition apparatus



Nov. 28, 1967 R. L. KONOPA PIEZOELECTRIC IGNITION APPARATUS 2 Sheets-Sheet 8 Filed Jan. 13, 1964 INVENTOR. RICHARD L. KONOPA ms ATTORNEY Patented Nov. 28, 1967 3,355,623 PIEZOELECTRIC IGNITION APPARATUS Richard L. Konopa, Anderson, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Jan. 13, 1964. Ser. No. 337,276 2 Claims. (Cl. 315-55) This invention relates to ignition apparatus for internal combustion engines and more particularly to ignition a-pparatus wherein the output voltage of a piezoelectric crystal is used to directly fire one or more spark plugs.

It is known in the ignition art that a spark plug of an internal combustion engine can be directly fired by the output voltage of a piezoelectric crystal without the use of ignition coils or batteries as in a conventional system. For the most part, the piezoelectric crystal is stressed by a cam and'follower mechanism. One type of cam and follower mechanism is shown in the Huiferd et al. patent 3,009,975. Other types of cam and follower mechanisms for stressing the crystals are shown in the Huiferd et al. patent 3,082,333, and in the Small et al. patent 3,094,108.

If the piezoelectric elements are overstressed in the type of apparatus just described, the danger of fracturing exists and if the elements are under stressed, insufficient output voltage is achieved for firing one or more spark plugs. It accordingly is one of the objects of this invention to periodically apply a substantially constant force to the piezoelectric crystal during operation of the ignition system. In carrying this object forward, the crystal is stressed by a spring and the force applied to the crystal is periodically relieved by a cam and follower mechanism which compresses the spring but not the crystal. The spring, therefore, applies a force to the crystal during a part of the cycle which remains substantially constant and thecrystal is therefore not overstressed to the point of fracture but is stressed sufiiciently to provide the required output voltage for firing a spark plug.

Another object of this invention is to provide apparatus for stressing a piezoelectric crystal wherein the force applied to the crystal remains substantially constant in spite of tolerances encountered during manufacturing or wear of the mechanical linkage during operation.

Still another object of this invention is to provide a a piezoelectric ignition system which is capable of firing a plurality of spark plugs and which is provided with means preferred embodiments of the present invention areclearlyf shown.

In the drawings:

FIGUREl illustrates a piezoelectric ignition system which includes a distributor shown in section, the cap and rotor of thedist'ributor being a section taken along line 1 1 of FIGURE 2,. FIGURE 2 is a'sect'ionalview taken along line 22 of FIGURE 1.

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 1.

FIGURE 4 is a sectional view taken along line 44 of FIGURE 3.

Referring now to the drawings and more particularly to FIGURE 1, the reference numeral designates an internal combustion engine having a plurality of spark plugs 12 for firing the combustable mixture of the engine. One side of the spark plugs are grounded whereas the opposite side of the spark plugs are connected respectively with spark plug wires 14, 16, 18 and 20. The spark plug Wires 14, 16, 18 and 20 are connected respectively with outer circumferentially spaced conductive inserts located in an annular cap 22 which is formed entirely of insulating material. Two of these conductive inserts are shown in FIGURE 1 and designated respectively by reference numerals 24 and 26 and are connected with wires 14 and 16. The other two conductive inserts which are not shown are located at 90 from the conductive inserts 24 and 26 and are connected with wires 18 and 20. The cap 22 hasa center electrode or insert 28 which is connected directly to ground. The electrode 28 operates to shunt unwanted voltages to ground as will become more readily apparent hereinafter.

The cap 22 is supported by a ring 30 which is formed of insulating material. If desired, the ring 30 and the cap 22 can be formed as one integral unit. The ring 30 carries a plurality of conductive terminals 32, 34, 36 and 38 which are illustrated in FIGURE 2. The terminals 32 and 36 are also illustrated in FIGURE 1.

The cap 22 and ring 30 are supported by a metal base 39. This metal base can be the housing of the engine 10 or can be a separate base as shown in FIGURE 1 which is secured to the housing of the engine 10 as with a conventional distributor.

The housing 39 supports a shaft 40 which is driven by the engine 10. The shaft 40 drives a double lobed cam 42. The lobes 42a and 42b of the cam 42 are located 180 from each other. The shaft 40 also drives a rotor part 44 which is formed of insulating material. The rotor 44 carries conductive parts 46 and 48 which are electrically connnected and which together form a discharging slider that connects the terminals 32 through 38 with the electrode 28 via the conductive ball 50. The rotor 44 also carries a conductive timing bar 52 which can electrically connect the various terminals 32 through 38 carried by the ring 30 ,with the outer terminals carried by the cap 22.

The housing 39 carries a support plate 54 which is used to support the piezoelectric crystals that supply the energy for firing the spark plugs 12. As seen in FIGURE 1 3, a pair of piezoelectric crystals or elements 56 and 58 are provided which have a common electrical terminal 60. These piezoelectric crystals are supported in a metal bracket 62 which in turn is supported by the plate 54. One end of the crystal 56 is engaged by a metal part 64 and one end of the crystal 58 is engaged by metal part 66. These metal parts are grounded and the crystals are connected in parallel with the output voltage being taken between conductor 60 and ground. A preloading screw 68-is provided as can be seen from FIGURES 3 and 4.

The piezoelectric crystals 56 and 58 are stressed by a spring 70 which is interposed between a spring retaining bracket 72 and an arm 74 which is pivoted at 76 to the support bracket 78 for another pair of crystals 78a and 78b. The arm 74 enagages an arm 80 which is pivoted at point 82 to the bracket 62. If desired, the bracket 62 may have an opening which can receive the outwardly bent section 82 of the lever 80.

The bracket 78 supports two piezoelectric crystals 78a and 78b which are identical with crystals 56 and 58. These crystals 78a and 78b are stressed by a similar system of levers and springs as is used to stress the crystals 56 and 58. Thus the mechanism for stressing the crystals carried by bracket 78 includes a lever 84, a lever 86 pivoted at 88, and a spring 90 interposed between lever 86 and the bracket 92 which like bracket 72, is secured to the plate 54. The pivot 88 is made to the plate 54 rather than to the case of a piezoelectric assembly as is the pivot 76 for the lever 74.

When the shaft 40 is rotated by the engine 10, the lobes 42a and 42b of the cam 42 will engage the cam follower levers '74 and 86 sequentially. When the lobes 42a and 42b are not engaging a lever, one of the springs will stress one of the pair of crystals. For example, in the position of cam 42 in FIGURE 3, the spring 70 will force the lever 74 counter-clock-wise. This will pivot the lever 80 clock-wise which will stress the crystals 56 and 58. When the crystals 56 and 58 are stressed, a voltage is applied to terminals 34 and 38 since these terminals are electrically connected with the center conductor 60 of the crystals 56 and 58. The electrical connections between the conductor 60 and the terminals 34 and 38 are not shown but they Would be of the same type as the electrical connections 96 and 98 for the conductor 94 shown in FIG- URE l which electrically connect the crystals 78a and 78b and terminals 32 and 36. As the cam continues to rotate, the time will come when the lever 74 is moved clock-wise in FIGURE 3 which relieves the spring force on the crystals 56 and 58 and a voltage of an opposite polarity will not be developed by the crystals 56 and 58.

In order to better understand the complete operation of this system, let it be assumed that the timing bar 52 is rotating clock-wise and is therefore approaching the terminal 36. The discharging slider formed of parts 46 and 48 which is 90 behind the timing bar 52 and is therefore approaching terminal 34. The terminal 36 as well as terminal 32 is electrically connected with the center terminal 94 of the crystals 78a and 78b carried by bracket 78 as is seen from FIGURE 1. As the timing bar 52 approaches terminal 36 and the discharging sliders 46 and 48 approach terminal 34, the crystals 78a and 78b will begin to be stressed by the spring 90 and are fully stressed so as to produce an output voltage when bar 52 becomes aligned with terminal 36 and terminal 24 of cap 22. Because of this, a voltage is produced in the crystals at the same time that timing bar 52 connects terminals 36 and 24 and one of the spark plugs 12 will now be fired via conductor 14.

When the bar 52 connects terminals 36 and 24, the slider comprised of parts 46 and 48 connect the terminal 34 with insert 28 to discharge the unwanted voltage from crystals 56 and 58 to ground.

As the cam 42 and rotor 44 continue to rotate, the crystals 56 and 58 will next be stressed by the spring 70 and the output voltage from these crystals will now be supplied to terminal 38 whereas the unwanted voltage from the crystals 78a and 78b will be discharged from terminal 36 and the slider formed of parts 46 and 48.

It will be appreciated that with the arrangement described, the four spark plugs 12 will all be fired during one revolution of cam 42 and during one revolution of the rotor 44. The cam and rotor are driven at one-half engine speed for a four stroke cycle engine.

From the foregoing, it can be seen that when the timing bar 52 is forming a conductive path to one of the spark plugs for the voltage generated by one pair of piezoelectric crystals, the slider formed of parts 46 and 48 is forming a discharge path for the other pair of piezoelectric crystals which at that time are being unstressed due to compression of one of the springs.

Although pairs of crystals have been illustrated as the device for supplying voltage to the spark plugs, it will be appreciated by those skilled in the art that one could be provided rather than two.

If a vacuum advance is desired for the system, the

by a vacuum motor relative to the shaft 40 which would provide a means of obtaining a vacuum advance for the ignition system of this invention. Centrifugal advance could be provided by providing a centrifugal advance mechanism between cam 42 and rotor 44 that would adjust rotor 44 relative to shaft 40 in response to speed.

While the embodiments of the present invention as herein disclosed constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. An ignition system for an internal combustion engine comprising, a plurality of spark plugs for said engine, first and second piezoelectric elements, a rotatable shaft, means driven by said internal combustion engine to rotate said rotatable shaft, first and second spring means for respectively applying a compressive stress to said piezoelectric elements, cam means driven by said rotatable shaft for sequentially compressing said spring means and unstressing said piezoelectric elements, a rotor driven by said rotatable shaft and first and second electrical conductor means carried by said rotor, one of said conductor means being operative to connect one of said piezoelectric elements with one of said spark plugs when said piezoelectric element is being stressed, the other of said conductor means being operative to simultaneously connect the other of said piezoelectric elements to ground whereby said other of said piezoelectric elements is electrically discharged.

2. Ignition apparatus for firing the spark plugs of an internal combustion engine comprising, a plurality of spark plugs for said engine, a plurality of piezoelectric elements, a spring means corresponding to each one of said piezoelectric elements for respectively applying a compressive stress to the corresponding piezoelectric element, rotatable cam means for sequentially compressing said spring means and unstressing said piezoelectric elements, a housing formed of insulating material, said housing having a center electrode, a first plurality of outer circumferentially spaced electrodes and a second plurality of outer circumferentiallyspaced electrodes each aligned with and spaced from a corresponding one of said first plurality of outer circumferentially spaced electrodes, means for connecting said first plurality of outer circumferentially spaced electrodes respectively with said spark plugs, means for connecting said second plurality of outer circumferentially spaced electrodes with said piezoelectric elements, means for connecting said center electrode with a discharging circuit and means rotatable with said cam means for sequentially connecting said piezoelectric elements with either saidv first plurality of outer circumferentially spaced electrodes or said center electrode.

References Cited UNITED STATES PATENTS 2,954,506 9/ 1960 Harkness 315--55 3,156,227 11/1964 Huiferd 315--55 X 3,208,443 9/ 1965 Hurwitz 3l0 8.7 X

JOHN W. HUCKERT, Primary Examiner.

D. O. KRAFT, J. SHEWMAKER, Assistant Examiners. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE COMPRISING, A PLURALITY OF SPARK PLUGS FOR SAID ENGINE, FIRST AND SECOND PIEZOELECTRIC ELEMENTS, A ROTATABLE SHAFT, MEANS DRIVEN BY SAID INTERNAL COMBUSTION ENGINE TO ROTATE SAID ROTATABLE SHAFT, FIRST AND SECOND SPRING MEANS FOR RESPECTIVELY APPLYING A COMPRESSIVE STRESS TO SAID PIEZOELECTRIC ELEMENTS, CAM MEANS DRIVEN BY SAID ROTATABLE SHAFT FOR SEQUENTIALLY COMPRESSING SAID SPRING MEANS AND UNSTRESSING SAID PIEZOELECTRIC ELEMENTS, A ROTOR DRIVEN BY SAID ROTATABLE SHAFT AND FIRST AND SECOND ELECTRICAL CONDUCTOR MEANS CARRIED BY SAID ROTOR, ONE OF SAID CONDUCTOR MEANS BEING OPERATIVE TO CONNECT ONE OF SAID PIEZOELECTRIC ELEMENTS WITH ONE OF SAID SPARK PLUGS WHEN SAID PIEZOELECTRIC ELEMENT IS BEING STRESSED, THE OTHER OF SAID CONDUCTOR MEANS BEING OPERATIVE TO SIMULTANEOUSLY CONNECT THE OTHER OF SAID PIEZOELECTRIC ELEMENTS TO GROUND WHEREBY SAID OTHER OF SAID PIEZOELECTRIC ELEMENTS TO GROUND WHEREDISCHARGED. 